Aqueous solution method for forming a hydrogel composition

ABSTRACT

Cross-linked polyvinyl polymers comprising charged groups and methods of making are disclosed. The polymers are effective and durable adsorbent of dyes from aqueous solutions. Also, a method of removal of dyes from contaminated water is disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a Continuation of U.S. application Ser. No.17/819,956, now allowed, having a filing date of Aug. 16, 2022, which isa Continuation of U.S. application Ser. No. 16/503,957, now U.S. Pat.No. 11,479,623, having a filing date of Jul. 5, 2019.

BACKGROUND OF THE INVENTION Field of the Disclosure

The present invention relates to a cross-linked polyvinyl matrix and usethereof for treating water to remove organic dyes.

Description of Related Art

The “background” description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description which may nototherwise qualify as prior art at the time of filing, are neitherexpressly or impliedly admitted as prior art against the presentdisclosure.

Water treatment is any process that improves water quality suitable fora specific end-use. The end use may include, but is not limited todrinking, industrial water supply, irrigation, river flow maintenance,water recreation or releasing the water to the environment. Watertreatment removes contaminants and undesirable components, or reducestheir concentration so that the water becomes fit for its intendedend-use. Water treatment is an essential process for healthy environmentthat can sustain all forms of life including human, animals, and plants.

The textile industry is a major contributor to environmental pollutionof water resources due to the release dyes into surface water, which inturn contaminates soil and underground water. Most synthetic dyes areinert and non-biodegradable aromatic compounds, and thus, accumulate inthe environment. Ingestion of contaminated water by humans and animalsmay be toxic and potentially carcinogenic. Several methods have beendeveloped and used to remove dyes from water including coagulation,adsorption, chemical oxidation, froth floatation, and adsorption. Theadsorption method is effective, efficient, and economical for treatmentof wastewater-contaminated with dyes.

U.S. Pat. No. 8,657,123B2 discloses a composite of a semipermeablemembrane comprising a silicon compound and a silicon free compound. Thesilicon compound has an ethylenically unsaturated group and ahydrolysable group both of which are directly bonded to the siliconatom. The silicon free compound has an ethylenically unsaturated groupand phosphonic, phosphoric, or sulfonic acid group. Among the siliconfree compound disclosed is vinylphosphonic acid (VPA). The semipermeablecomposite of U.S. Pat. No. 8,657,123B2 is intended for use in adesalination process and not for removing dyes from contaminated water.

U.S. Pat. No. 9,956,314B2 discloses an adhesive composition for bondingto bone and bone-like structure which comprises a polymerizablemultifunctional acidic monomer, one or more multifunctional monomerswith one or more ethylenically unsaturated groups, an organicallymodified calcium phosphate salt, and polymerization initiator. Among themultifunctional acidic monomers disclosed arebis[2-(methacryloyloxy)ethyl] phosphate (BMEP) and VPA. U.S. Pat. No.9,956,314B2 does not disclose the use of the polymer to remove dyes fromcontaminated water.

US20100280169A1 discloses an ampholytic co-polymer comprising at leastone macromolecular chain B and at least one part A bonded to chain B.Chain B comprises a quaternary ammonium group, and part A is derivedfrom anionic monomer. Among part A monomers disclosed are VPA orethylenically unsaturated phosphate esters. US20100280169A1 does notdisclose the use of the ampholytic co-polymer in removing dyes fromcontaminated water.

Kim et al. [J. Pow. Sour. (2015) 293, 539-547] disclose a poly(aryleneether sulfone) semi-interpenetrating polymer network membrane formed bypolymerizing VPA and BMEP in a solution of N,N-dimethylacetamidecomprising poly(arylene ether sulfone). The membrane displays highproton conductivity and is useful for the construction ofelectrochemical fuel cells. Kim et al. do not disclose the use of thepolymer in removing dyes from contaminated water.

Elliot et al. [Polymer (2003) 44 (14) 3775-3784] disclose a series ofpolymers containing different ratios of methyl methacrylate and2-(dimethylamino)ethyl methacrylate synthesized by free radicalpolymerization. The copolymers were converted to salts with acidmonomers such as methylacrylic acid, methacryloyloxyethylphosphate, andvinyl phosphonic acid. Elliot et al. do not disclose any particular usefor the copolymers or their salts.

Nakhjiri et al. [Inter. J. Biol. Macromol. (2018) 117, 152-166] disclosea hydrogel polymer prepared by polymerizing acrylic acid, VPA, andN-maleyl chitosan. The polymer is able to adsorb methylene blue andcrystal violet from aqueous solution.

Nakhjiri et al. [J. Poly. Res. (2018) 25, 244] disclose the synthesispoly(acrylamide-co-2-acrylamido-2-methyl-1-propane sulfonic acid)/sodiummontmorillonite hydrogel nanocomposite with different amounts of BMEP asa cross linker which is formed by free radical polymerization. Thehydrogel nanocomposite was used in a method to remove crystal violet,methylene blue, and methyl red from aqueous solution. Based on thethermodynamic studies, Nakhjiri et al. disclosed a method of treatingwater contaminated with dyes comprising the spontaneous adsorption ofdye by the nanocomposite followed by desorption of the dye from thenanocomposite by ethanol.

None of the above mentioned polymers is shown to be an effective anddurable adsorbent of dyes from aqueous solution. It is therefore oneobject of the disclosure is to provide a durable crosslinked polyvinylmatrix comprising ionizable groups as an efficient adsorbent of dyesfrom aqueous medium.

The foregoing paragraphs have been provided by way of generalintroduction, and are not intended to limit the scope of the followingclaims. The described embodiments, together with further advantages,will be best understood by reference to the following detaileddescription taken in conjunction with the accompanying drawings.

SUMMARY OF THE INVENTION

One aspect of the invention is directed crosslinked polyvinyl polymerprepared by polymerizing a vinyl compound having chemical formula I:

in the presence of a cross linking compound having formula II:

wherein R₁ is phosphonate, phosphate, sulfonate, carboxylate orCH₂—NRR′; R and R′ are independently hydrogen, methyl, ethyl, propyl; orisopropyl; R₂, R₃, and R₄ are independently hydrogen, sulfonate,carboxylate, phosphonate, optionally substituted methyl, ethyl, propyl,optionally substituted cycloalkyl, optionally substituted aryl orheteroaryl; R₅ and R₆ are independently acryloyl, methylacryloyl, vinyl,propenyl, acetyleneyl and methylenyl acetylenic; and X is phosphate,sulfate, oxygen, keto group, carbamide, carbamate, carboxamide, orcarbonate; and the cross linking compound of formula II is in an amountin the range of 2 mol. % to 60 mol. % of the total molar amount of thevinyl compound of formula I and the cross linking compound of formulaII.

In a preferred embodiment, the vinyl compound of formula I is selectedfrom the group consisting of vinylphoshonic acid (VPA), vinylsulfonicacid, acrylic acid, 2-methyl acrylic acid, malieic acid, and fumaricacid.

In another preferred embodiment, the vinyl compound of formula I is VPA.

In another preferred embodiment, the cross linking compound of formulaII is bis[2-(methyacryloyloxy)ethyl] phosphate (BMEP),bis[2-(methyacryloyloxy)ethyl] carbonate, orbis[2-(methyacryloyloxy)ethyl] sulfate.

In another preferred embodiment, the cross linking compound of formulaII is BMEP.

In another preferred embodiment, the cross linking compound of formulaII is in an amount in the range of 10 mol. % to 50 mol. % of the totalmolar amount of the vinyl compound of formula I and the cross linkingcompound of formula II.

In a more preferred embodiment, the cross linking compound of formula IIis in an amount of about 40 mol. % of the total molar amount of thevinyl compound of formula I and the cross linking compound of formulaII.

In another preferred embodiment, the vinyl compound of formula I is VPAand the cross linking compound of formula II is BMEP.

In another preferred embodiment, the cross linking compound of BMEP isin an amount in the range of 10 mole % to 50 mol. % of total molaramount of VPA and BMEP.

In another preferred embodiment, the cross linking compound of BMEP isabout 40 mol. % of total molar amount of VPA and BMEP.

Another aspect of the invention is directed to a method of making across linked polymer comprising:

-   -   mixing aqueous solution of vinyl compound having chemical        formula I:

and an aqueous solution of a cross linking compound having formula II:

-   -   optionally adding a polymerization initiator to the aqueous        solution to form a mixture, and    -   initiating the polymerization reaction;        wherein R₁ is phosphonate, phosphate, sulfonate, carboxylate, or        CH₂—NRR′; R and R′ are independently hydrogen, methyl, ethyl,        propyl; or isopropyl; R₂, R₃, and R₄ are independently hydrogen,        sulfonate, carboxylate, phosphonate, optionally substituted        methyl, ethyl, propyl, optionally substituted cycloalkyl,        optionally substituted aryl or heteroaryl; R₅ and R₆ are        independently acryloyl, methylacryloyl, vinyl, propenyl,        acetylenyl, and acetylenic methylene; and X is phosphate,        sulfate, oxygen, keto group, carbamide, carbamate, carboxamide,        or carbonate; and the cross linking compound of formula II is in        an amount in the range of 2 mol. % to 60 mol. % of the total        molar amount of the vinyl compound of formula I and the cross        linking compound of formula II.

In a preferred embodiment, the polymerization initiator is selected fromthe group consisting of an azo compound, a ketone, organic peroxide, andinorganic peroxide.

In a more preferred embodiment, the azo compound isazobis(2-methylpropionamidine dihydrochloride).

In another preferred embodiment, initiating the polymerization comprisesheating the mixture at a temperature in the range of 50 to 150° C.

In a more preferred embodiment, initiating the polymerization reactioncomprises heating the mixture at a temperature in the range of 70 to 90°C.

In another preferred embodiment, initiating the polymerization reactioncomprises irradiating the mixture with ultraviolet/visible light.

In another preferred embodiment, the compounds of formula I, formula II,and the polymerization initiator are VPA, BMEP, andazobis(2-methylpropionamidine dihydrochloride), respectively.

Another aspect of the invention is directed to a method of removing adye from contaminated water comprises:

-   -   contacting the contaminated water with the cross linked polymer        of the invention, allowing the polymer to be in contact with for        a time in the range of 5 minutes to 60 minutes, and    -   removing the polymer.

In another preferred embodiment, the polymer contains a cross linkingcompound in an amount in the range of 10 mole % to 50 mole % of thetotal molar amount of vinyl compound and the cross linking compound.

In another preferred embodiment, the dye is one or more of methyleneblue, methyl orange, basic violet, parabase, bromophenol blue andnatural ink.

In another preferred embodiment, the method further comprisesreactivating the polymer by treatment with an organic solvent.

In a more preferred embodiment, the solvent is an alcohol selected fromthe group consisting of methanol, ethanol, propanol, isopropanol, andbutanol and isomers thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 shows scheme for the synthesis of a polyvinylphosphonicacid/bis[2-(methyacryloyloxy)ethyl]phosphate (PVPA-BMEP) matrix.

FIG. 2 shows FTIR spectra of PVPA cross-linked with 5 mole %, 10 mole %,20 mole %, and 40 mole % of BMEP.

FIG. 3 shows thermogravimetric spectra of PVPA cross-linked with (a) 5mole %, (b) 10 mole %, (d) 20 mole %, and (c) 40 mole % of BMEP.

FIG. 4 shows an SEM image of PVPA cross-linked with 5 mole % of BMEP.

FIG. 5 shows an SEM image of PVPA cross-linked with 10 mole % of BMEP.

FIG. 6 shows an SEM image of PVPA cross-linked with 20 mole % of BMEP.

FIG. 7 shows an SEM image of PVPA cross-linked with 40 mole % of BMEP.

FIG. 8 shows the adsorption characteristics of PVPA cross-linked with 5mole %, 10 mole %, 20 mole %, and 40 mole % of BMEP at an initialconcentration of 100 mg/L methylene blue,

FIG. 9 shows the adsorption characteristics of PVPA cross-linked with 5mole %, 10 mole %, 20 mole %, and 40 mole % of BMEP at an initialconcentration of 250 mg/L methylene blue.

FIG. 10 shows the adsorption characteristics of PVPA cross-linked with 5mole %, 10 mole %, 20 mole %, and 40 mole % of BMEP at an initialconcentration of 500 mg/L methylene blue.

FIG. 11 shows the adsorption characteristics of PVPA cross-linked with 5mole %, 10 mole %, 20 mole %, and 40 mole % of BMEP at an initialconcentration of 1000 mg/L methylene blue.

FIG. 12 shows the color of aqueous solutions comprising 100 mg/Lmethylene blue after incubation for three hours with PVPA-BMEP matrix:(A) PVPA crossed-linked with 40 mole % BMEP, (B) PVPA crossed-linkedwith 20 mole % BMEP, (C) PVPA crossed-linked with 10 mole % BMEP, and(D) PVPA crossed-linked with 5 mole % BMEP in an amount of 1000 mg/L. Eshows the color of an aqueous solution 100 mg/L methylene blue.

FIG. 13 shows a Langmuir isotherm model for the adsorption of methyleneblue on PVPA-BMEP (40% PVPA).

DETAILED DESCRIPTION

Embodiments of the present disclosure will now be described more fullyhereinafter with reference to the accompanying drawings, in which some,but not all embodiments of the disclosure are shown. The presentdisclosure will be better understood with reference to the followingdefinitions.

All publications mentioned herein are incorporated herein by referencein full for the purpose of describing and disclosing the methodologies,which are described in the publications, which might be used inconnection with the description herein. Nothing herein is to beconstrued as an admission that the inventors are not entitled toantedate such disclosure by virtue of prior disclosure. Also, the use of“or” means “and/or” unless stated otherwise. Similarly, “comprise,”“comprises,” “comprising” “include,” “includes,” and “including” areinterchangeable and not intended to be limiting.

Unless otherwise specified, “a” or “an” means “one or more”.

Terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention.

The headings (such as “Background” and “Summary”) and sub-headings usedherein are intended only for general organization of topics within thepresent invention, and are not intended to limit the disclosure of thepresent invention or any aspect thereof. In particular, subject matterdisclosed in the “Background” may include novel technology and may notconstitute a recitation of prior art. Subject matter disclosed in the“Summary” is not an exhaustive or complete disclosure of the entirescope of the technology or any embodiments thereof. Classification ordiscussion of a material within a section of this specification ashaving a particular utility is made for convenience, and no inferenceshould be drawn that the material must necessarily or solely function inaccordance with its classification herein when it is used in any givencomposition.

It will be further understood that the terms “comprises” and/or“comprising,” when used in this specification, specify the presence ofstated features, steps, operations, elements, and/or components, but donot preclude the presence or addition of one or more other features,steps, operations, elements, components, and/or groups thereof.

As used herein, the term “and/or” includes any and all combinations ofone or more of the associated listed items and may be abbreviated as“/”.

Links are disabled by deletion of http: or by insertion of a space orunderlined space before www. In some instances, the text available viathe link on the “last accessed” date may be incorporated by reference.

As used herein in the specification and claims, including as used in theexamples and unless otherwise expressly specified, all numbers may beread as if prefaced by the word “substantially”, “about” or“approximately,” even if the term does not expressly appear. As usedherein, the term “about” refers to an approximate number within 20% of astated value, preferably within 15% of a stated value, more preferablywithin 10% of a stated value, and most preferably within 5% of a statedvalue. For example, if a stated value is about 8.0, the value may varyin the range of 8±1.6, ±1.0, ±0.8, ±0.5, ±0.4, ±0.3, ±0.2, or ±0.1.

Disclosure of values and ranges of values for specific parameters (suchas temperatures, molecular weights, weight percentages, etc.) are notexclusive of other values and ranges of values useful herein. It isenvisioned that two or more specific exemplified values for a givenparameter may define endpoints for a range of values that may be claimedfor the parameter. For example, if Parameter X is exemplified herein tohave value A and also exemplified to have value Z, it is envisioned thatparameter X may have a range of values from about A to about Z.Similarly, it is envisioned that disclosure of two or more ranges ofvalues for a parameter (whether such ranges are nested, overlapping ordistinct) subsume all possible combination of ranges for the value thatmight be claimed using endpoints of the disclosed ranges. For example,if parameter X is exemplified herein to have values in the range of 1-10it also describes subranges for Parameter X including 1-9, 1-8, 1-7,2-9, 2-8, 2-7, 3-9, 3-8, 3-7, 2-8, 3-7, 4-6, or 7-10, 8-10 or 9-10 asmere examples. A range encompasses its endpoints as well as valuesinside of an endpoint, for example, the range 0-5 includes 0, >0, 1, 2,3, 4, <5 and 5.

As used herein, the words “preferred” and “preferably” refer toembodiments of the technology that afford certain benefits, undercertain circumstances. However, other embodiments may also be preferred,under the same or other circumstances. Furthermore, the recitation ofone or more preferred embodiments does not imply that other embodimentsare not useful, and is not intended to exclude other embodiments fromthe scope of the technology.

As used herein, the word “include,” and its variants, is intended to benon-limiting, such that recitation of items in a list is not to theexclusion of other like items that may also be useful in the materials,compositions, devices, and methods of this technology. Similarly, theterms “can” and “may” and their variants are intended to benon-limiting, such that recitation that an embodiment can or maycomprise certain elements or features does not exclude other embodimentsof the present invention that do not contain those elements or features.

The description and specific examples, while indicating embodiments ofthe technology, are intended for purposes of illustration only and arenot intended to limit the scope of the technology. Moreover, recitationof multiple embodiments having stated features is not intended toexclude other embodiments having additional features, or otherembodiments incorporating different combinations of the stated features.Specific examples are provided for illustrative purposes of how to makeand use the compositions and methods of this technology and, unlessexplicitly stated otherwise, are not intended to be a representationthat given embodiments of this technology have, or have not, been madeor tested.

As used herein, the term “substituted” refers to at least one hydrogenatom that is replaced with a non-hydrogen group, provided that normalvalences are maintained and that the substitution results in a stablecompound. When a substituent is noted as “optionally substituted”, thesubstituents are selected from the exemplary group including, but notlimited to, halo, hydroxyl, alkoxy, oxo, alkanoyl, aryloxy, alkanoyloxy,amino, alkylamino, arylamino, arylalkylamino, disubstituted amines (e.g.in which the two amino substituents are selected from the exemplarygroup including, but not limited to, alkyl, aryl or arylalkyl),alkanylamino, aroylamino, aralkanoylamino, substituted alkanoylamino,substituted arylamino, aubstituted aralkanoylamino, thiol, alkylthio,arylthio, arylalkylthio, alkylthiono, arylthiono, aryalkylthiono,alkylsulfonyl, arylsulfonyl, arylalkylsulfonyl, sulfonamide (e.g.—SO₂NH₂), substituted sulfonamide, nitro, cyano, carboxy, carbamyl (e.g.—CONH₂), substituted carbamyl (e.g. —CONHalkyl, —CONHaryl,—CONHarylalkyl or cases where there are two substituents on one nitrogenfrom alkyl, aryl, or alkylalkyl), alkoxycarbonyl, aryl, substitutedaryl, guanidine, heterocyclyl (e.g. indolyl, imidazoyl, furyl, thienyl,thiazolyl, pyrrolidyl, pyridyl, pyrimidiyl, pyrrolidinyl, piperidinyl,morpholinyl, piperazinyl, homopiperazinyl and the like), substitutedheterocyclyl and mixtures thereof and the like.

As used herein, the term “alkyl” unless otherwise specified refers toboth branched and straight chain saturated aliphatic primary, secondary,and/or tertiary hydrocarbons of typically C₁ to C₁₀, preferably C₁ toC₆, more preferably C₂ to C₃, and specifically includes, but is notlimited to, methyl, trifluoromethyl, ethyl, n-propyl, isopropyl,n-butyl, sec-butyl, isobutyl, t-butyl, pentyl, isopentyl, neopentyl,hexyl, isohexyl, 3-methylpentyl, 2,2-dimethylbutyl, and2,3-dimethylbutyl.

As used herein, the term “cycloalkyl” refers to cyclized alkyl groups.Exemplary cycloalkyl groups include, but are not limited to,cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, norbornyl, andadamantyl. Branched cycloalkyl groups such as exemplary1-methylcyclopropyl and 2-methylcyclopropyl groups are included in thedefinition of cycloalkyl as used in the present disclosure.

The term “alkenyl” refers to a straight, branched, or cyclic hydrocarbonfragment containing at least one C═C double bond. Exemplary alkenylgroups include, without limitation, 1-propenyl, 2-propenyl (or “allyl”),1-butenyl, 2-butenyl, 3-butenyl, 1-pentenyl, 2-pentenyl, 3-pentenyl,4-pentenyl, 1-hexenyl, 2-hexenyl, 3-hexenyl, 4-hexenyl, 5-hexenyl,1-heptenyl, 2-heptenyl, 3-heptenyl, 4-heptenyl, 5-heptenyl, 6-heptenyl,1-octenyl, 2-octenyl, 3-octenyl, 4-octenyl, 5-octenyl, 6-octenyl,7-octenyl, 1-nonenyl, 2-nonenyl, 3-nonenyl, 4-nonenyl, 5-nonenyl,6-nonenyl, 7-nonenyl, 8-nonenyl, 1-decenyl, 2-decenyl, 3-decenyl,4-decenyl, 5-decenyl, 6-decenyl, 7-decenyl, 8-decenyl, and 9-decenyl.

The term “alkynyl” refers to a straight or branched hydrocarbon fragmentcontaining at least one CC triple bond. Exemplary alkynyl groupsinclude, without limitation, ethynyl, 1-propynyl, 2-propynyl (i.e.,propargyl), 1-butynyl, 2-butynyl, 3-butynyl, 1-pentynyl, 2-pentynyl,3-pentynyl, 4-pentynyl, 1-hexynyl, 2-hexynyl, 3-hexynyl, 4-hexynyl,5-hexynyl, 1-heptynyl, 2-heptynyl, 3-heptynyl, 4-heptynyl, 5-heptynyl,6-heptynyl, 1-octynyl, 2-octynyl, 3-octynyl, 4-octynyl, 5-octynyl,6-octynyl, 7-octynyl, 1-nonynyl, 2-nonynyl, 3-nonynyl, 4-nonynyl,5-nonynyl, 6-nonynyl, 7-nonynyl, 8-nonynyl, 1-decynyl, 2-decynyl,3-decynyl, 4-decynyl, 5-decynyl, 6-decynyl, 7-decynyl, 8-decynyl, and9-decynyl.

The term “alkoxy” refers to a straight or branched chain alkoxyincluding, but not limited to, methoxy, ethoxy, propoxy, isopropoxy,butoxy, isobutoxy, secondary butoxy, tertiary butoxy, pentoxy,isopentoxy, hexyloxy, heptyloxy, octyloxy, nonyloxy, and decyloxy.

As used herein, the term “aryl” unless otherwise specified refers tofunctional groups or substituents derived from an aromatic ringincluding, but not limited to, phenyl, biphenyl, napthyl, anthracenyl,thienyl, and indolyl.

The term “arylalkyl”, as used herein, refers to a straight or branchedchain alkyl moiety having 1 to 8 carbon atoms that is substituted by anaryl group as defined herein, and includes, but is not limited to,benzyl, phenethyl, 2-methylbenzyl, 3-methylbenzyl, 4-methylbenzyl,2,4-dimethylbenzyl, 2-(4-ethylphenyl)ethyl, 3-(3-propylphenyl)propyl,and the like.

The term “alkanoyl”, as used herein, refers to an alkyl group ofspecified number of carbon atoms that is bound to an oxygen atom througha double bond. Exemplary alkanoyl groups include, but are not limitedto, formyl, acetyl, propanoyl, butyryl, and hexanoyl.

The term “aroyl” as used in this disclosure refers to an aromaticcarboxylic acyl group includes, for example, benzoyl, 1-naphthoyl, and2-naphthoyl.

The term “halogen”, as used herein, means fluorine, chlorine, bromine,and iodine.

As used herein a “polymer” or “polymeric resin” refers to a largemolecule or macromolecule, of many repeating subunits and/or substancescomposed of macromolecules. As used herein a “monomer” refers to amolecule or compound that may bind chemically to other molecules to forma polymer. As used herein the term “repeat unit” or “repeating unit”refers to a part of the polymer or resin whose repetition would producethe complete polymer chain (excluding the end groups) by linking therepeating units together successively along the chain. The process bywhich monomers combine end to end to form a polymer is referred toherein as “polymerization” or “polycondensation”, monomers are moleculeswhich can undergo polymerization, thereby contributing constitutionalrepeating units to the structures of a macromolecule or polymer. As usedherein “resin” or “polymeric resin” refers to a solid or highly viscoussubstance or polymeric macromolecule containing polymers, preferablywith reactive groups. As used herein a “copolymer” refers to a polymerderived from more than one species of monomer and are obtained by“copolymerization” of more than one species of monomer. Copolymersobtained by copolymerization of two monomer species may be termedbipolymers, those obtained from three monomers may be termed terpolymersand those obtained from four monomers may be termed quarterpolymers,etc. As used herein, “cross-linking”, “cross-linked” or a “cross-link”refers to polymers and resins containing branches that connect polymerchains via bonds that link one polymer chain to another. The cross-linkmay be an atom, a group of atoms, or a number of branch points connectedby bonds, groups of atoms, or polymer chains. In the majority of cases,a cross-link is a covalent structure or covalent bond but the term mayalso describe sites of weaker chemical interactions, portioncrystallites, and even physical interactions and entanglements. Thecross-linking can alter the physical and mechanical properties of thepolymer. Cross-linking may be formed by chemical reactions that areinitiated by heat, pressure, change in pH, and/or radiation, with orwithout the presence of a cross-linking agent and/or catalyst.

One aspect of the invention is directed to a crosslinked polyvinylpolymer prepared by polymerization of a vinyl compound in the presenceof a cross linking compound. The vinyl compound can be any compoundcomprising a double bond and a charged group in aqueous solution at pHin the range of 2-11, preferably, 3-10, preferably 4-9, preferably 5-8.Examples of charged groups include, but not limited to phosphonatephosphate, sulfonate, sulfate, carboxylate, and ammonium group. Thecross linking compound may be any compound which is able to cross-linkpolyvinyl polymer such as those described herein below.

In some embodiments, the vinyl compound has the chemical formula I:

wherein R₁ is phosphonate, phosphate, sulfonate, carboxylate orCH₂—NRR′; R and R′ are independently hydrogen, methyl, ethyl, propyl; orisopropyl; R₂, R₃, and R₄ are independently hydrogen, sulfonate,carboxylate, phosphonate or phosphate, optionally substituted alkylgroup such as, but not limited to methyl, ethyl, propyl, optionallysubstituted cycloalkyl such as but not limited cyclobutyl, cyclopentyl,or cyclohexyl, optionally substituted aryl such as phenyl, o-, m-, orp-phenyl carboxylic acid, o-, m-, or p-aminopbenzyl, and the like,optionally substituted heteroaryl such as but not limited to pyrrole,imidazole, triazole, thiophene, furan, and the like. The vinyl compoundof formula I is present in co-polymerized form in the crosslinkedpolyvinyl polymer in an amount in the range of 30 mol. % to 95 mol. % ofthe total molar amount of formula I and II.

A cross linking compound of formula II is present in co-polymerized formin the crosslinked polyvinyl polymer in an amount in the range of 2 mol.% to 60 mol. % of the total molar amount of formula I and II. Thecross-linking compound is a monomer of formula II having two or morepolymerizable moieties separated by a linker comprising a hydrophilicmoiety such as, but not limited to phosphate, sulfate, oxygen, ketogroup, carbamide, carbamate, carboxyamide, carbonate, and the like. Asused herein the word “polymerizable moiety” is a functional moiety in apolymerization reaction, preferably in a free radical initiatedpolymerization reaction. Examples of polymerizable moieties include, butare not limited to vinyl, acryloyl, methacryloyl, acrylamide,acetylenic, and the like. Examples of cross-linker compounds include,but are not limited to diallyl hydrogen phosphate,bis-(2-methylacryloyloxyethyl)phosphate, divinyl carbonate, diallylcarbonate, bis(2-methylallyl)carbonate, diallyl urea, divinylsulfate,diallyl sulfate, diethylene glycol divinyl ether, piperazinediacrylamide, N,N′-ethylenebisacrylamide, ethyleneglycoldiallyl ether,ethylene glycol dimethacrylate, trimethyloylpropane trimethacrylate,diethyleneglycol dimethacrylate, bis(glycerol dimethacrylate) phosphate,glycerol dimethylacrylate, divinyl ketone, and the like.

In some embodiments, the cross linking compound has chemical formula II:

wherein R₅ and R₆ are independently acryloyl, methylacryloyl, vinyl,propenyl, acetyleneyl and methylenyl acetylenic, and X is phosphate,sulfate, oxygen, carbonyl group, carbamide, carbamate, carboxamide, orcarbonate. Examples of compounds of formula II include but are notlimited to bis[2-(methyacryloyloxy)ethyl] phosphate (BMEP),bis[2-(methyacryloyloxy)ethyl] carbonate, bis[2-(methyacryloyloxy)ethyl]sulfate, divinyl ketone, and the like.

In some preferred embodiments, cross-linked vinyl polymer comprises anamount of vinyl compound of formula I in the range of 30-95 mole %,preferably 35-80 mole %, preferably 40-60 mole %, and preferably 40-50mole % of the total molar amount of the vinyl compound of formula I andthe cross linking compound of formula II.

In some preferred embodiments, the cross linking compound of formula IIis present in co-polymerized form in the crosslinked polyvinyl polymerin an amount in the range of 1 mole % to 60 mole %, preferably 5 mole %to 55 mole %, preferably 10 mole % to 50 mole %, preferably 15 mole % to45 mole %, preferably 20 mole % to 40 mole %, and preferably about 40mole % of the vinyl compound of formula I.

In a preferred embodiment, the cross linked polymer of the invention ispolyvinylphosphonic acid-bis[2-(methyacryloyloxy)ethyl] phosphatepolymer prepared by polymerizing vinlyphosphonic acid (VPA) in thepresence of bis[2-(methacryloyloxy)ethyl] phosphate (BMEP), wherein BMEPis present in co-polymerized form in the crosslinked polyvinyl polymerin an amount in the range of 5 mole % to 55 mole %, preferably 10 mole %to 50 mole %, preferably 15 mole % to 45 mole %, and preferably 20 mole% to 40 mole % of the total molar amount of VPA and BMEP. In aparticularly preferred embodiment, the amount of BMEP is about 40 mole %of the total molar amount of VPA and BMEP.

Another aspect of the invention is directed to a method of making thecross-linked polyvinyl polymer of the invention. The method comprisesfree radical co-polymerization of a vinyl compound with a cross-linkingcompound. The polymerization reaction may be initiated by several meansincluding but not limited to thermochemical, photochemical,electrochemical, sonication, ionizing radiation, redox reaction andplasma which are described herein below.

Thermal and photochemical initiations are the most commonly usedinitiating methods. Thermal and photochemical polymerization initiatorsare chemical compounds that produce free radicals on decomposition byheating or irradiation with UV/visible light. They may be organic orinorganic compounds. Peroxides and azo compounds are well-knowninitiators as they produce free-radicals generated by heating orirradiation with UV/visible light. The rate of formation of free radicalfrom peroxide is highly dependent on the composition of the reactionmixture, solvent, temperature, and pH.

Organic peroxides have a peroxide bond (—O—) which is readily cleaved togive two oxygen radicals. The oxy-radicals are unstable anddisproportionate to more stable carbon radicals. For example, di-t-butylperoxide (tBuOOtBu) produces two t-butoxy radicals (tBuO·) whichdisproportionate to methyl radicals (CH₃·) and acetone. Similarly,benzoyl peroxide ((PhCOO)₂) generates two benzoyloxy radicals (PhCOO·),each of which loses carbon dioxide produce a phenyl radical (Ph·).Inorganic peroxides function in similar fashion to organic peroxides.Many polymers are often produced from alkenes upon initiation withperoxydisulfate salts. In solution, peroxydisulfate dissociates to twosulfate radicals anion. The sulfate radical anion adds to one of thecarbon atom of a double bond leading to the formation of a sulfate esterbond and a free radical center at the second carbon of the double bondwhich initiate the polymerization free radical chain reaction.

Azo compounds (R—N═N—R′) are precursors of two carbon-centered radicals(R· and R′·) produced by heating or irradiating with UV/visible lightwith concomitant release of nitrogen gas. For example, heating2,2′-azobisisobutyronitrile (AIBN) yield two isobutyronitrile radicalsaccording to the equation:

In some embodiments of the method, one or more thermal initiators may beused to initiate the polymerization reaction. Examples of thermalinitiator include, but are not limited to tert-amyl peroxybenzoate,4,4-azobis(4-cyanovaleric acid), 1,1′-azobis(cyclohexanecarbonitrile)(ABCN), 2,2′-azobisisobutyronitrile (AIBN), benzoyl peroxide,2,2-bis(tert-butylperoxy)butane, 1,1-bis(tert-butylperoxy)cyclohexane,2,5-bis(tert-butylperoxy)-2,5-dimethylhexane, 2,5-Bis(tert-butylperoxy)2,5-dimethyl-3-hexyne, bis(1-(tert-butylperoxy)-1-methylethyl)benzene,1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, tert-butylhydroperoxide, tert-butyl peracetate, tert-butyl peroxide, tert-butylperoxybenzoate, tert-butylperoxy isopropyl carbonate, cumenehydroperoxide, cyclohexanone peroxide, dicumyl peroxide, lauroylperoxide, 2,4-pentanedione peroxide, peracetic acid, potassiumpersulfate, ammonium persulfate, and sodium persulfate.

In some other embodiments, photoinitiation may be preferred. Examples ofphotoinitiators include, but not limited to azo Compounds such as butnot limited to 4,4′-azobis(4-cyanovaleric acid),1,1′-azobis(cyclohexanecarbonitrile), 2,2′azobis(2-methylpropionitrile), azobisisobutyronitrile,2,2′-azobis(2-methylpropionitrile),2,2-dimethoxy-1,2-diphenylethan-1-one,2-hydroxy-2-methyl-1-phenylpropanone, 1-hdroxy-cyclohexylphenylketone,benzophenone, isopropyl thioxanthone, 2-ethylhexyl-(4-N,N-dimethylamino)benzoate, and ethyl-4-(dimethylamino)benzoate.

The amount of thermal or photochemical initiator may vary depending onthe nature of the vinyl compound, the cross linking compound, thedesired reaction temperature, the rate of thermal or photochemicaldecomposition of the initiator, and the solvent, if present. In someembodiments, the amount of the initiator is in the range of 0.01-5.0mole %, preferably 0.05-4.0 mole %, preferably 0.1-3.0 mole %,preferably 0.5-3.0 mole %, preferably 0.8-3.0 mole %, preferably 1.0-2.0mole %, and preferably about 1% of the total molar amount of formula Iand II.

In some other embodiments, other polymerization initiation methods,which do not require chemical initiators, may be used to produce thepolymer of the invention. In some embodiments, the polymerizationreaction may be initiated by electrolysis of a solution containing bothmonomer(s) and electrolyte. A monomer molecule will receive an electronat the cathode to become a radical anion, and a monomer molecule willgive up an electron at the anode to form a radical cation. The radicalions then initiate free radical (and/or ionic) polymerization. Such aprocess is particularly useful for coating a permeable surface with thepolymer of the invention.

Another method for initiating a polymerization reaction by free radicalis by sonicating a monomer(s) or solution thereof with high-intensityultrasound at frequencies beyond the range of human hearing (16 kHz).Initiation results from the effects of cavitation, i.e., the formationand collapse of cavities in the liquid. The collapse of the cavitiesgenerates local high temperatures and pressures leading to excitedelectronic states, which in turn results in homolytic cleavage of acovalent bond and formation of free radicals.

Another method of initiating polymerization by free radicals involvesirradiating a reaction mixture comprising a monomer and a co-monomerwith ionizing radiations such as α, β, γ, or X-ray to produce freeradicals and thereby initiate the polymerization reaction.

Yet another free-radical initiation method including a redox reactionmay be utilized in the method of the invention. The initiation methodinvolves reduction of hydrogen peroxide or an peroxy alcohols byiron(II) ion. Other reductants such as Cr²⁺, V²⁺, Ti³⁺, Co²⁺, and Cu¹⁺can be employed in place of ferrous ion in many instances.

The method of the invention comprises preparing a reaction mixturecomprising a vinyl compound, a cross-linking compound, and optionally aninitiator. In some embodiments, the reaction mixture may contain asolvent. The solvent may be any solvent that does not interfere with thepolymerization reaction. Examples of suitable solvents include, but notlimited to water, methanol, ethanol, propanol, butanol, diethyl ether,ethyl methyl ether, and diethyl ether. In some embodiments, the reactionmixture is homogeneous, i.e., the vinyl compound and the cross-linkingcompound, and initiator, if present, are all in one phase such as beingsoluble in a solvent. In some other embodiment, the reaction mixturecomprises an aqueous phase, water insoluble vinyl compound and/or crosslinking compound, and initiator soluble in one of the monomers droplets.Alternatively if the initiator is soluble in water, a reaction mixturecomprising suspension of the vinyl compound and cross linking compoundsuspended in an aqueous solution of the initiator may be prepared andthe reaction is initiated as described above

In some embodiments, the reaction mixture contains a thermal initiator.In such a case, the reaction may be heated at a temperature in the rangeof 50 to 150° C., preferably 60 to 120° C., preferably 70 to 100° C.,and preferably 70 to 75° C. In some other embodiments, the reactionmixture contains a photo initiator. In such a case, the reaction mixturemay be irradiated with UV/visible light at a wave length at which theinitiator absorb light.

In some other embodiments, the polymerization reaction may be carriedout without any solvent. In such a case, a vinyl compound, a crosslinking compound, and optionally initiator are mixed and the mixtureheated or irradiated as described above.

A preferred embodiment of the method comprises preparing an aqueoussolution of VPA, BMEP, and azo-bis-(2-methylpropionamidine)dihydrochloride as an initiator to form a reaction mixture. The amountof VPA in the reaction mixture is in the range of 30-95 mole %,preferably 35-80 mole %, preferably 40-60 mole %, and preferably 40-50mole % of the total molar amount of VPA and BMEP. The amount of BMEP inthe reaction mixture is at least 5 mole %, preferably 10 mole %,preferably 15 mole %, preferably 20 mole %, preferably 25 mole %,preferably 30 mole %, preferably 35 mole %, preferably 40 mole %,preferably 45 mole %, and preferably 50 mole % of the total molar amountof VPA and BMEP. In one preferred embodiment of the method, the amountof BMEP in the reaction mixture is in the range of 40-45 mole % of thetotal molar amount of VPA and BMEP. The amount of initiatorazo-bis-(2-methylpropionamidine) dihydrochloride is in the range of0.01-5.0 mole %, preferably 0.05-4.0 mole %, preferably 0.1-3.0 mole %,preferably 0.5-3.0 mole %, preferably 0.8-3.0 mole %, preferably 1.0-2.0mole %, and preferably about 1 mole % of VPA. The reaction mixture isheated to a temperature in the range of 60-80° C., preferably 65-75° C.,and preferably about 70° C. In some embodiments, the cross-linkedpolyvinyl polymer may contain other monomers to modify the propertiespolymer such as the charge distribution and the charge density of thepolymer in relatively small amount. The modifying monomer may be presentin an amount in the range of 1-20 mole %, preferably 3-18 mole %,preferably 5-15 mole %, 7-12 mole %, preferably about 10 mole % of thetotal molar amount of VPA and BMEP.

Another aspect of the invention is directed to a method of removing dyesfrom contaminated water. The method comprises contacting thecontaminated water with the cross-linked polyvinyl polymer of theinvention for a time sufficient to substantially adsorb the dye on thecross-linked polyvinyl polymer and thereby remove the dye from thewater, preferably for a time in the range of 5-150 min, 10-120 min,preferably 15-100 min, 20-90 min, preferably 25-80 min, preferably 30-60min, and preferably 35-40 min. In a particularly preferred embodiment,the contaminated water is contacted with the polymer for about 30 min.The contacting of water with cross-linked polyvinyl polymer of theinvention may be a part of remediation process to remove a dye fromwaste water from a textile manufacturing facility and release the waterto the environment. Alternatively, it may be a step in a multistepprocess to purify water for human and animal consumption, oragricultural use.

In some embodiments, the cross-linked polyvinyl polymer may be addeddirectly to the water and removed after a time in the range of 5-60 min,preferably 10-50 min, preferably 15-40 min, and preferably about 30 min.The amount of cross-linked polyvinyl polymer added to the water ishighly dependent on the amount of dye in the water and the mole % of thecross-linker of the cross-linked polyvinyl polymer. In some embodiment,the amount of cross-linked polyvinyl polymer added to the water is atleast 10 mg/L, 20 mg/L, 30 mg/L, 40 mg/L, 50 mg/L, 50 mg/L, 60 mg/L, 70mg/L, 80 mg/L, 90 mg/L, 100 mg/L, 200 mg/L, 300 mg/L, 400 mg/L, 500mg/L, 600 mg/L, 700 mg/L, 800 mg/L, 900 mg/L, 1.0 g/L, 1.5 g/L, 2.0 g/L,2.5 g/L and more. The process may be carried out once or repeated for asmany times as needed. In some embodiment, the process is carried out atleast once, twice, trice, or more times until the water becomescolorless.

In an alternative embodiments of the method, a column may be packed witha bed of material comprising the cross-linked polyvinyl polymer of theinvention alone or in combination with ion exchange resin and/orhydrophobic resin and flowing the water through the bed at a flow ratethat allow the water to be in contact with the polymer of the inventionfor at least 5 min, 10 min, 20 min, 30 min, 40 min, 50 min, or 60 min.

The water treatment method of the invention for the removal of dye mayinclude an additional step(s) to release the bound dyes from the polymerand thereby regenerate the cross-linked polymer of the invention forfurther use. The regeneration step comprises treating the used polymerwith an organic solvent in which the polymer is insoluble or has lowsolubility. Examples of solvents include, but not limited to alcoholssuch as but not limited to methanol, ethanol, propanol, isopropanol,butanol, isobutanol, t-butano and the like; chlorinated hydrocarbonssuch as but not limited to dichloromethane, chloroform,carbontetrachloride, dichloroethane; diols such as ethylene glycol orpropylene glycol, hydrocarbons such as but not limited to hexane,cyclohexane, pentane, cyclopentane, benzene, toluene, petroleum ether,and the like; and ethers such as but not limited to dimethyl ether,diethyl ether, and methyl ethyl ether.

Any single dye or combination of dyes contaminating waste water may befully or partially removed by the method of the invention including butnot limited to those dyes derived from acridine, anthraquinone,arylmethan, azo compounds, phthalocyanine, quinone-imine compounds,azine compounds, indamine compounds, indophenol, oxazin compounds,oxazone compounds, thiazine, thiazole, safranine, and xanthene. In someembodiment, the method of the invention may be used to remove more thanone dye which may be present in the contaminated water. Examples ofparticular dyes include but not limited to methylene blue, methylorange, basic violet, parabase, bromophenol blue, natural ink, alzarin,7,14-dibenzpyrenequinone, dibromoanthanthrone, indigo, and combinationthereof.

Example 1

Vinylphosphonic acid (VPA) was polymerized in the presence of severalmolar fractions of bis[2-(methacryloyloxy)ethyl] phosphate (BMEP) toproduce crosslinked polyvinylphohonic acid hydrogels (PVPA-BMEP) (FIG. 1). The mole ratio of BMEP was varied from 5 to 40% with respect to VPA.Azobis(2-methylpropionamidine dihydrochloride) was used as initiator andthe polymerization was carried out in water at 70° C. In a typicalpreparation, 1.0 g (9.2 mmole) of VPA, 1.2 g (3.7 mmole) of BMEP, 0.025g (0.09 mmole) of Azobis(2-methylpropionamidine dihydrochloride) weredissolved in deionized ionized water by adjusting the pH to about 9, andthe solution is heated at 70° C. for two hours. The precipitated polymeris filtered and washed with ether, and dried in an oven. Table 1summarizes the content of the final product.

TABLE 1 Content of PVPA-BMEP preparations Preparation PVPA, g BMEP, gPVPA-BMEP-5 mol % 1.0 0.15 PVPA-BMEP-10 mol % 1.0 0.30 PVPA-BMEP-10 mol% 1.0 0.60 PVPA-BMEP-20 mol % 1.0 1.20

Example 2

Characterization of the Cross-Liked Polymer

FIG. 2 shows PVPA-BMEP cross-1 inked polymer matrices with differentmole percentages of BM EP. The characteristic broad peak appearedbetween 990-910 cm⁻¹ can be assigned to the (P—O)—H stretching ofphosphonic acid groups of the PVPA. The peak at 1150 cm⁻¹ belongs to P—Ostretching of BMEP and becomes more intense with increasing the molefraction of BMEP in the matrix. Phosphonic acid group gives additionalbroad band in the region of 1635 cm⁻¹. The carboxyl group (C═O)stretching is clearly observed at 1720 cm⁻¹ and becomes more intense asthe mole fraction of BMEP is increased. The narrow and weak band at 2880cm⁻¹ and 2900 cm⁻¹ are due to the C—H stretching vibrations in methyland methylene groups of BMEP. The broadening within 3300-2000 cm⁻¹ canbe attributed to hydrogen bonding network formation among phoshonic acidgroups [Sinirlioglu et al. (2014) “Novel composite polymer electrolytemembranes based on poly(vinyl phosphonic acid) and poly(5-(methacrylamido)tetrazole)” Polymer Engineering& Science 55(2):260-269—incorporated herein by reference in its entierty].

FIG. 2 b depicts TGA graph of PVPA/BMEP with different compositions. Thethermograms illustrate several steps weight change in the temperaturerange of measurement. The first step is the weight lost up 100° C. thatcan be attributed to loss of absorbed humidity. The second step whichbegins at 120° C. and continues until 220° C. can be attributed tocondensation reactions among phosphonic acid groups (Sinirlioglu etal.). The degradation of BMEP occurs at a temperature between 220-430°C. Above 430° C., further degradation of the cross-linked polymer occurs[Vilela et al. (2018) Poly(bis[2-(methacryloyloxy)ethyl]phosphate)/Bacterial Cellulose Nanocomposites: Preparation,Characterization and Application as Polymer Electrolyte Membranes.Applied Sciences 8 (7)].

The SEM micrographs of FIGS. 4-7 show the surface morphology of thefinal purified materials.

Example 3

Crosslinked polyvinylphosphonic acid (PVPA) comprising 5 mol %, 10 mole%, 20 mole %, and 40 mole % of bis[2-(methyacryloyloxy)ethyl] phosphate(BMEP) as a cross linker were tested for the adsorption of methyleneblue (MB) as a model dye at concentrations of 100, 250, 500, and 1000mg/mL. FIGS. 8-11 show time dependent adsorption of differentconcentration of methylene blue by cross-linked PVPA with 5 mole %, 10mole %, 20 mole %, and 40 mole % with BMEP. The time dependentadsorption study of the dye by PVPA-BMEP shows the time required toreach equilibrium is 30 minutes and is independent from mole % of thecross linker. FIG. 12 shows the color intensity of MB after 3 hoursincubation of 100 mg/L MB with 1000 mg/L of PVPA cross linked with (A)40 mole %, (B) 20 mole %, (C) 10 mole %, and (D) 5 mole % of BMEP. Thecolor intensity of the initial methylene blue concentration of 100 mg/Lwithout any PVPA-BMEP is shown in (E) in FIG. 12 . Dye adsorption byPVPA comprising 40 mole % BMEP cross linked was significantly moreeffective (98.2%) in dye removal compared to those cross linked with 20mole %, 40 mole %, and 5 mole BMEP.

FIG. 13 shows Langmuir isotherm model for adsorption of MB on PVPA-BMEP(40%). The amount of MB adsorbed on the PVPA-BMEP at equilibrium Qe(mg/g) is calculated as follows:

$Q_{e} = \frac{\left( {C_{0} - C_{e}} \right)V}{M}$

Where: C₀ and C_(e) are the initial and equilibrium concentrations of MBin the solution (mg/L), respectively; V is the volume of the workingsolution (L); and M is the mass of the PVPA-BMEP in the solution (g).

Rafatullah et al. [J. Hazard. Mater. (2010) 177, 70-80] reviewed about185 published papers directed to the use of potentially low-costadsorbents including agricultural wastes, industrial solid wastes,biomass, clays minerals and zeolites for the removal of MB from wastewaters of textile, paper, printing and other industries. The reviewindicated that the “teak wood bark” displayed the highest MB adsorptioncapacity of 915 mg/g reaching equilibrium within 6 hours which wasreported by McKay et al. [Water Air Soil Pollut. (1999) 114, 423-438].Wang et al. [Chem. Eng. J. (2013) 228, 132-139] investigated adsorptionof methylene blue (MB) on an alginate-based nanocomposite hydrogelenhanced by organo-illite/smectite clay. They found that thenanocomposite can adsorb MB with a higher adsorption capacity (1843.46mg/g) in 30 minutes. Most recently, Yao et al. [J. Hazard. Mater. (2015)292, 90-97] reported an efficient adsorption of MB on porous magneticpolyacrylamide microspheres. The microspheres can adsorb methylene bluewith high efficiency, with an adsorption capacity of 1977 mg/g andcontact time of 150 minutes.

The maximum adsorption capacity (q_(max))=1/slope=1/0.0002=5,000 mg/gwith significant linear correlation value of 0.996. The maximumadsorption capacity (q_(max)) determined by the Langmuir isotherm modelreached to 5,000 mg MB/g of PVPA-BMEP which is about 2.5 time greaterthan those previously reported. The adsorption characteristics showedthat an adsorption time of about 30 minutes is a quite fast dye removalperiod with respect to previously conducted studies.

The invention claimed is:
 1. Aqueous solution method for forming ahydrogel composition, comprising: mixing an aqueous solution of avinylphosphonic acid having chemical formula I:

and an aqueous solution of bis[2-(methyacryloyloxy)ethyl] phosphate(BMEP) to form an aqueous mixture; and initiating a polymerizationreaction in the aqueous mixture by adding an initiator selected from thegroup consisting of an azo compound, a ketone, and an organic peroxideto form a polymerization reaction mixture, heating the polymerizationreaction mixture to form the hydrogel composition, wherein the hydrogelcomposition comprises a cross linked polyvinyl polymer; wherein R₁ isphosphonate; and R₂, R₃, and R₄ are independently hydrogen, sulfonate,carboxylate, phosphonate, optionally substituted methyl, ethyl, propyl,optionally substituted cycloalkyl, or optionally substituted aryl orheteroaryl; wherein the BMEP is present in the cross linked polyvinylpolymer in an amount of about 40 mol % based on the total molar amountof the vinylphosphonic acid of formula I and the BMEP; and wherein thecross linked polyvinyl polymer consists essentially of polymerized unitsof the vinylphosphonic acid having chemical formula I and the BMEP. 2.The method of claim 1, wherein the initiating comprises heating thepolymerization reaction mixture at a temperature in the range of 50 to150° C.
 3. The method of claim 1, wherein the initiating comprisesirradiating the polymerization reaction mixture with ultraviolet/visiblelight.
 4. The method of claim 1, wherein the polymerization reaction isinitiated with azobis(2-methylpropionamidine dihydrochloride).
 5. Themethod of claim 4, wherein the initiating comprises heating thepolymerization reaction mixture at a temperature in the range of 70 to90° C.
 6. The method of claim 1, wherein the vinylphosphonic acid offormula I is vinyl phosphonic acid.
 7. The method of claim 1, whereinthe cross linked polyvinyl polymer consists of polymerized units of thevinyl phosphonic acid of formula I cross-linked with the BMEP.
 8. Themethod of claim 1, wherein the BMEP is present in the cross linkedpolyvinyl polymer in an amount of 40±4 mol. %.